Hi, I have some changes to the attachment system which will allow XWiki to handle much larger attachments without memory exhaustion. I have found that there are some places where I cannot make any changes because the code is not in XWiki but rather in JRCS.
XWiki versions attachments by creating a JRCS node for the XML version of each version of each attachment. This means that memory consumption improvements hit a hard wall at 2 * 2 * 1.3 * the size of the attachment. base-64 encoding for XML increases the size by 1.3 times, storage as a String (array of 16 bit chars) doubles the size and the need to copy the String doubles the size again. The second issue is that the database and JDBC do not handle multiple hundreds of megabytes in a single query well. If I try to attach a 500MB attachment with attachment versioning disabled, my changes allow the attachment to be streamed to the database but postgresql is not able to save it. I am able to attach a 256MB attachment but with 512MB of heap space, the attachment cannot be loaded from the database because JDBC lacks the necessary streaming functionality. An option which I am now considering is adding a binary table to the database schema. The table would contain a composite id made of the id of the data and the part number of that entry, and a data column slightly smaller than 1MB (default max_allowed_packet in mysql). All interaction with this table would go through a storage engine which would require InputStreams and OutputStreams and the streams would be written and read by the storage mechanism which would ID tag them and break them up into parts to be sent to the database individually. WDYT? Caleb _______________________________________________ devs mailing list [email protected] http://lists.xwiki.org/mailman/listinfo/devs
